1. Field of the Invention
The present invention is a method for irradiating a chemically machinable light-sensitive glass with a parallel bundle of ultraviolet rays to form tapered holes or slits in the light-sensitive glass.
2. Description of the Prior Art
Holes or slits are often formed in a chemically machinable light-sensitive glass by irradiating the glass with ultraviolet rays through a mask placed on the surface of the glass. After the irradiation, the glass is heated causing fine lithium metasilicate (SiO.sub.2 -Li.sub.2 O) crystals to grow in the irradiated area. When the thus irradiated and heated glass is treated with a hydrofluoric acid solution, the crystal area dissolves at a faster rate than the non-irradiated area of the glass forming holes or slits in the irradiated areas. The above method is used to make perforations, engravings, channels and cuttings in chemically machinable light-sensitive glass.
In accordance with the conventional method for irradiation with ultraviolet rays which has heretofore been used to perforate chemically machinable light-sensitive glass, a parallel bundle of ultraviolet rays is applied vertically or obliquely to the glass plate with a mask mounted thereon. The mask has openings corresponding in shape and dimension to holes to be formed in the glass plate. In the conventional method, the light source and the light-sensitive glass plate are always kept in the same relative positional relationship. Thus, the diameter of the holes finally formed in the glass plate by application of hydrofluoric acid solution treatment is uniform in the direction of thickness of the glass even though the holes may be oriented vertically or obliquely relative to the glass plate. Typical holes formed by the conventional method are shown in FIG. 1(a). As can be seen, it is not possible to produce tapered holes such as those shown in FIG. 1(b) wherein the hole diameter increases in the direction of thickness of the glass plate according to the conventional method.